The recovery of crude oil from a rock formation usually takes place in several stages. The first phase of production resulting from the natural energy of the oil in place; oil goes freely outside the well because the difference of pressure between the reservoir and atmospheric pressure. This initial recovery, called primary recovery, represents generally about 5 to 20% of the average amount of oil in the rock formation. The secondary and tertiary recovery consists of drilling several wells around the depleted rock formation, at least one injection well where a flooding fluid is injected under pressure and at least one producing well in which oil is recovered. The flooding fluid forms a front of migration that will move toward the oil producing well, because of its non miscibility properties with oil. This technique is called enhanced oil recovery (EOR for Enhancing Oil Recovery) and can generally get 25 to 75% oil. Tertiary recovery differs from the secondary recovery by the nature of injected fluid. In the secondary recovery, aqueous liquid such as brine or fresh water has been injected through a well whereas in the tertiary recovery, additional compounds have been mixed in the injecting aqueous fluid before the injecting and flooding steps.
There are three main techniques for the tertiary recovery. One is based on the injection of a flooding fluid comprising polymers, the other one is based on the injection of a flooding fluid comprising surfactants and in the last one, the flooding fluid comprises a mixture of polymers and surfactants.
Surfactants have been used as additional compounds in order to lower the interfacial surface tension (IFT) of the aqueous fluid and in order to enable the aqueous fluid to form emulsions and/or microemulsions with the oil in the reservoir. The formations of mixtures and/or microemulsions dislodges the entrapped oils in the rock formations through IFT reduction and solubilization of oil in the aqueous surfactant solutions thereby increasing the recovery of oil from subterranean formations. However, the surfactant fluids have less viscosity than the oil, so their effectiveness in pushing the oil from the formations is limited.
Synthetic polymers have been used for increasing the viscosity of the aqueous fluids. These polymers are for example polyacrylamide, polyvinylpyrrolidone or polyvinyl-sulphonate and their derivatives. Natural polymer such as polysaccharides extracted from grains such as the Guar gum or algae such as alginates or carrageenans or from the biopolymers produced by fermentation initiated by bacteria or mushrooms are used for their high viscosifying capacity (HYDROCOLLOIDS, CEH Marketing Research Report, Ray K. Will, October 2007).
However, the addition of natural polysaccharides polymers in an aqueous fluid presents one substantial disadvantage. Natural polysaccharides commonly are poorly injectable due to the presence of residue of synthesis or poorly solvated part of the chain that may impair the permeability of the near wellbore injection zone.
The purpose of this invention is to overcome the drawback of prior art.
It is therefore an object of this invention to provide a new flooding fluid for enhancing oil recovery operations having good injectivity properties.
It is yet a further object of the present invention to have a flooding fluid that adsorbs moderately on the formation.
It is further an object of the invention to provide a new flooding fluid that exhibits high resistance to mechanical degradations.
It is also an object of the present invention to provide a flooding fluid having good thermal stability properties.